How to Use Ad Hominem
So, you’re in a debate with someone and it doesn’t look like you’re going to win this one based on the merit of your argument alone. Cue the logical fallacies. The key to winning an argument with logical fallacies, is to be subtle with the fallacies. “Poisoning the well” may not work if the audience realizes you poisoned it.
Example
A young woman mentions that the fashion and modeling industry are sexist. Her opponent replies, “You just think that because you’re fat.”
Her weight is so far from the topic of fashion, modeling, sexism and society that the audience is likely to detect the pointlessness and mean-ness of the reply.
Instead, her opponent could have replied, “After taking feminist theory, it’s probably hard not to see sexism in EVERYTHING.”
This is equally irrelevant as the “you’re fat” reply, but not obviously so. Essentially, the girl is being called paranoid, and no argument is being made, but the relation of her feminist theory class to her perspective on fashion and modeling seems justified.
Avoiding Ad Hominem
In any case, it’s better to avoid Ad Hominem by preparing and researching all the points for and against your position. This way, you will be ready for your opponents arguments with facts and relevant information.
When to Use Ad Hominem
Ad hominem is most used in debate and advertising. You may be able to get away with using it in an essay, but you’re not supposed to. You would not want to see it in a supposedly objective text, such as a scientific magazine, textbook, or newspaper. Logical fallacies have a bad name because they can be used to mislead people (and usually are).
However, logical fallacies can also appear in fiction, between characters, showing that one character is illogical, mean, ruthless, clever, or deceptive. There are lots of real people who use logical fallacies every day to get their way. And be aware that using unfair prejudices against a character often makes the audience sympathetic to that character.